1. Field of the Invention
The present invention relates to a system and method for unthrottled intake air control for an internal combustion engine.
2. Terminology
Engine Displacement
This is used herein to mean the sum of displacements of all of cylinders of an engine. xe2x80x9cEngine displacementxe2x80x9d and xe2x80x9cdisplacement of an enginexe2x80x9d are synonyms. In the description, the reference character xe2x80x9cVOL#xe2x80x9d is used to represent the xe2x80x9cengine displacementxe2x80x9d.
Volumetric Airflow Ratio
This is used herein to mean a ratio between the volumetric airflow admitted to cylinders of an engine through a given effective flow cross sectional area and the maximum volumetric airflow admitted to all of the cylinders of the engine through the maximum effective flow cross sectional area. The maximum effective flow cross sectional area is provided when all the cylinder of the engine are in operation with a throttle in an intake manifold kept at WOT position. In the description, the reference characters xe2x80x9cQH0STLxe2x80x9d, xe2x80x9cTQH0ST1xe2x80x9d, xe2x80x9cTQH0ST2xe2x80x9d, xe2x80x9cTQH0STxe2x80x9d, xe2x80x9cQH0STL*xe2x80x9d and xe2x80x9cTQH0ST*xe2x80x9d are used to represent the xe2x80x9cvolumetric airflow ratioxe2x80x9d and this ratio is expressed in terms of percentage (%).
Opening Area for Unit Volumetric Airflow
This is used herein to mean a value resulting from dividing (opening area for requested airflow) by (engine displacement VOL#) and then by (engine speed NE). In the description, the reference characters xe2x80x9cGADNVLxe2x80x9d, xe2x80x9cTGADNV1xe2x80x9d, xe2x80x9cTGADNV2xe2x80x9d, xe2x80x9cTGADNVxe2x80x9d, xe2x80x9cGADNVL*xe2x80x9d and xe2x80x9cTGADNV*xe2x80x9d are used to represent xe2x80x9copening area for unit volumetric airflow.xe2x80x9d
Most commercially available automotive engines use a throttle valve to control engine load by throttling intake air. As a result, there is a compromise between the best fuel economy, emission control and engine power conditions.
Potentially, better fuel economy, emission control and engine output benefits can be realized and particularly at part load conditions if the engine pumping losses are eliminated or minimized. This can be realized by using unthrottled operation coupled with a phase shifting of the intake valve event from a normal schedule to close within a range of either early or late in the engine cycle as a function of air charge to be trapped.
JP-A 10-37727 discloses a system for eliminating cylinder to cylinder torque variation by controlling intake valve close times in such a manner that air charges trapped may become equal to each other.
Control strategies for unthrottled intake air control have not evolved to a satisfactory level. Control strategies may imitate control strategies for throttled intake air control. However, the ability of the controller to adjust the intake valve open and/or close times or timings independently from the crankshaft position and the accelerator pedal position offers a great flexibility in setting engine response performance within a range between aggressive response and sluggish response.
To provide optimal driving comfort, it is desirable to provide unthrottled intake air control coupled with appropriate engine response performance.
It is an object of the present invention to provide a system and method for unthrottled intake air control which can provide different engine response performances to meet different requests.
According to one aspect of the present invention, there is provided a method for unthrottled control of intake air for an internal combustion engine, the engine having at least one combustion chamber provided with intake means, wherein the opening and closing times of the intake means are adjustable entirely independently from the crankshaft position to control intake air supplied to the combustion chamber, the method comprising:
determining a first portion of requested intake airflow, which first portion requests a first engine response performance;
determining a second portion of said requested intake airflow, which second portion requests a second engine response performance;
processing said first and second portions of said requested intake airflow to make contributions to said first and second engine response performances, respectively, and to provide processed requested airflow;
determining an intake means activation command in response to said processed requested airflow; and
providing said intake means activation command to the intake means to provide an engine response performance combining said first engine response performance with said second engine response performance.